Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 M3W EML/CEL - P0173 - Help?

Hi All

I have a 2019 M3W.
It had its last service in July this year.

The EML has come on and reads fault code P0173 which is "Rear Adaptive Max Limit".
The light isn't a permanent fixture. Sometimes it lasts for 20 miles, sometimes it's only on for a quarter of a mile.
Sometimes I might shut the car off with the light on but upon firing the car up again its off and vice versa...

The car runs ok, idles ok, pulls well.

Any ideas?

To my knowledge, the car is a factory 2019 car with the Euro3 spec.
It does have a high-flow exhaust. No idea if that is factory though.

Any ideas?

Cheers

Ed

Probably over filled the fuel tank which leads to over fuelling till the fuel level drops and the fumes canister and vent line has run out of liquid petrol. Try disconnecting the battery for a couple of minutes to clear the fault codes and see if it comes back or clear it from Pro-Tune if you have a laptop and the software. Failing that it could be a dodgy Lambda sensor or injector on the right-hand cylinder.
And welcome to the forum!

I thought that might be the case - I have spent a lot of time browsing the forums to figure it out.
But I've done about 100 miles now and I assumed that would have been enough to clear the canister.


I'll have to monitor it for now and see if it disappears. Just strange that it comes and goes so frequently.

The car runs perfectly so I presume it is safe to drive.

Thanks.

As the car runs the ECU adapts the air/fuel mixture based on the readings from the lambda sensors. There is a limited range of adjustment and the code you have simply means it hit the limit at one point.

It's not unusual for the MIL light to come on occasionally and, as above, over filling can set it off. Also, depending on the type of high flow exhaust you might occasionally hit the limit.

The code should clear eventually but it can take 10 or more engine starts or need to be cleared in Protune. If the car's running OK it's safe to carry on driving.

Do you have a stock Euro3?

I gave up on the engine warning light and just check the engine regularly and ignore the light.

You can get a P0170 or P0173 "front/ rear adaptive maxed out" code if your fuel pump is not delivering 58psi, or it is not being regulated to 58psi. If the Check Engine Lamp warning persists it is worth checking the fuel pressure at the test point on the RH injector. If it is low the ECU will extend the injector open time to get the correct mixture until it runs out of range. If the pressure is low and you rectify this you will need to clear the adaptive maps from the ECU as they will have compensated for the low pressure delivery.

The usual cause of low pressure is the pump. Have you got the original fuel pump fitted or a Walbro one? If it's still the original it is worth replacing anyway as it will fail at some point. Instructions are available in the resources "sticky" at the top of this forum. The pressure regulator/ filter above the rear wheel can also cause low pressure but this is rare. They have been known to leak from corrosion around the clamp, worth checking and protecting with tape to prevent dissimilar metal corrosion.

I would concur with Planenut, the fuel pump must go. It will not necessarily just go out all at once but might give subtle little hints in not running in best tune. Mine did that until it died completely, fortunately it left me in the pub parking lot 1 blok from my home.

Thanks all for the replies and advice.

At this stage, I'm inclined to rule out overfilling the fuel. It's been about 100 miles now since I fuelled it. The EML has come on and gone off 2 dozen times since then.

It's difficult to really spot any reason why it's going on/off at the time but it does seem to go off after sustained engine running at a lower RPM and it does seem to come on after more spirited driving and higher revving (say, above 3.5k). I'll seldom go over 4,250rpm as the car is so torquey you really don't need to.

Having said that, correlation doesn't equal causation and it could be a coincidence.

I can only presume it's related to the High Flow exhaust or like others have said possibly a fuel pump issue.
But the car does run absolutely perfectly.

It had a full service at the factory in June so I am surprised nothing was picked up then.

It will run perfectly with a failing fuel pump until it either fails totally or the ECU runs out of compensating adjustment. It is unlikely that anyone would pick this up on a service as it is not normal to check the fuel pressure on that and it may well have been running well at that point. It is advisable to change the standard pump for a Walbro anyway. It's not a big job and will save you a lot of trouble in the future. The engine runs better with a free flowing exhaust and will run within the capabilities of a locked ECU, I doubt that is your problem.

yeah, mine is only off at idle. 18000 miles later and it runs fine